Electro-hydraulic brake valves may be used in earth-moving equipment, such as track-type tractors and other types of earth-moving machines, to apply and release braking devices. Electronic controllers may control the brake valves by transmitting brake command currents to the brake valve in response to detecting actuation or release of a braking control device by an operator of the earth-moving machine. In other implementations wherein the machine may be autonomously operated using GPS or other navigation technology, the controller may determine when to actuate or release the braking device based on the position, speed and direction of motion of the machine, and automatically transmit the brake command currents. The brake valve responds to the brake command currents by changing the pressure within the braking device to tighten or loosen the braking device as commanded.
When operating properly, the brake command currents will cause the brake valve to create pressure within an acceptable range of pressures to effectuate the commanded braking. However, the brake valve and braking device may not always respond as expected. The pressure created in response to the braking signal may lie outside the acceptable pressure range. If the pressure is too great, the machine may stop suddenly, or the tubes and seals carrying the hydraulic fluid may rupture. If the pressure is too low, the machine may not stop at all or at least as quickly as desired. The improper response by the brake valve and braking device may be a sign of degradation in the system or a potential failure mode that causes loss of brake performance.
Control systems and failure detection apparatus for brake systems are known in the art. For example, U.S. Pat. No. 7,540,572, entitled “Failure Detection Apparatus,” teaches a failure detecting apparatus for detecting a failure of a solenoid-operated control valve having a coil, a valve chamber, and a movable member which is movable, while changing a volume of the valve chamber, by an electromagnetic drive force produced upon supplying of an electric current to the coil so that the solenoid-operated control valve is selectively placed in one of an open state thereof and a closed state thereof. The failure detecting apparatus includes a pressure-change detecting device which detects a change of a pressure on at least one of a high-pressure side and a low-pressure side of the solenoid-operated control valve, and a failure detecting portion which detects that the solenoid-operated control valve has failed when a change of the pressure detected by the pressure-change detecting device upon controlling of the electric current supplied to the coil is smaller than a change of the pressure that results from a change of the volume of the valve chamber caused by a movement of the movable member. The control disclosed in the publication relates only to failures where the actual pressure produced by the control valve is less than expected, but actual pressures exceeding the expected pressure may also be undesirable.
In another example, U.S. Pat. Appl. Publ. No. 2004/0012258, entitled “Brake Control Apparatus with Solenoid Valve,” teaches, in a brake control apparatus, a range of change in a hydraulic pressure with respect to an amount of current applied by a drive signal from a control circuit of a normally-open (N/O) valve provided in a hydraulic path that extends from a hydraulic pressure generation source to a wheel cylinder is set to be smaller than a range of change in a hydraulic pressure with respect to an amount of current applied to a normally closed (N/C) valve provided in a hydraulic path that extends from the wheel cylinder to a reservoir. Accordingly, it is possible to decrease the hydraulic pressure which is generated when the amount of current is minutely varied in the N/O valve, thereby enhancing controllability of the hydraulic pressure. This enables highly accurate hydraulic control. The teaching of the reference focuses on accurate hydraulic control in the braking system, but does not relate to identifying over-pressure and under-pressure responses in the braking system and executing a strategy for responding to such conditions.
In view of the above, a need exists for an electro-hydraulic brake valve monitoring system for detecting under-pressure and over-pressure situations in braking systems and alerting an operator of the vehicle or taking other corrective actions in response. A further need exists in such a brake valve monitoring system for taking into account and basing the responsiveness of the system on the effects of internal and external factors affecting the speed of reaction of the vehicle to correct issues in the braking system.